docs: def convert_ruptureCollection(self, node):
          """
          :param node: a ruptureCollection node
          :returns: a dictionary grp_id -> EBRuptures
          """
          coll = {}
          for grpnode in node:
              grp_id = int(grpnode['id'])
              coll[grp_id] = ebrs = []
              for node in grpnode:
                  rup = self.convert_node(node)
                  rup.serial = int(node['id'])
                  sesnodes = node.stochasticEventSets
                  n = 0  # number of events
                  for sesnode in sesnodes:
                      with context(self.fname, sesnode):
                          n += len(sesnode.text.split())
                  ebr = source.rupture.EBRupture(rup, 0, 0, numpy.array([n]))
                  ebrs.append(ebr)
          return coll